Anomalous magnetism and 209Bi nuclear spin relaxation in Bi4Ge3O12 crystals

V.G. Orlov1, E.A. Kravchenko2, Tetsuo Asaji3, G.S. Sergeev1, Yu.F. Kargin4, A.N. Vasil’ev5, O.S. Volkova5

1Russian Research Center “Kurchatov Institute”, Moscow, Russia 2Institute of General and Inorganic Chemistry, Moscow, Russia 3Department of Chemistry, College of Humanities and Sciences, Nihon University, Tokyo, Japan 4State Institute of Metallurgy and Material Science, Moscow, Russia5Lomonosov Moscow State University, Moscow, Russia

BikAlOmXn (A =Al, B, Ge, Ba; X = Cl, Br)

Hloc ≤ 250 G ; E.A. Kravchenko, V.G. Orlov, M.P. Shlykov

Russian Chem. Rev. 75 (2006)

E.A. Kravchenko, V.G. Orlov et al., JETP Lett. 86 (2007)

α-Bi2O3

V.I. Nizhankovskii, A.I. Kharkovskii, V.G. Orlov

Ferroelectrics 279 (2002) T = 4.2 K; H || c; ▲– ZFC; □ – FC, H = 284 Oe; Δ – FC, H = 566 Oe;

0

100

200

300

400

500

1000 2000 3000 4000

M (10 G cm /g)-5 3.

H (Oe)

α-Bi2O3

V.I. Nizhankovskii, A.I. Kharkovskii, V.G. Orlov Ferroelectrics 279 (2002)

150

2

1

0 50 100H (kOe)

-2 2P (10 esu/cm )

In2Te powder 77K In(1) ν2=15.12 MHz

Bi4Ge3O12

E.A. Kravchenko, V.G. Orlov et al., JETP Lett. 86 (2007)

E.A. Kravchenko, Yu.F. Kargin, V.G. Orlov, T. Okuda, K. Yamada, JMMM 224 (2001)

Bi4Ge3O12

, Pure, H=0 Pure, H=30 Oe Gd-doped Nd-doped Pr-doped

T2 μsec 50 100 220 400 400

2( , , ) ( , , ) exp( / )ext extI H T A H T T

E.A. Kravchenko, V.G. Orlov et al., JETP Lett. 86 (2007)

Bi4Ge3O12

1 1 11 1 1( ) ( ) ;l eT T T

1 1 1 1 11 1 1 1 1

1 1 11 1

( ) ( ) ; ( ) ; ( ) ;

; exp( / );

nl e l e e

e e s e

T T T T b T T K

T T a T

V.G. Orlov T. Asaji E.A. Kravchenko et al. JETP 137 (2010)

Gd-doped Bi4Ge3O12

Nd-doped Bi4Ge3O12

0 0 0 0 4 4 0 0 4 42 2 4 4 4 4 6 6 6 6

ˆCEFH B O B O B O B O B O

0

5

20

25

Δ

meV

Conclusion

• A strong influence of minor amounts of paramagnetic dopand atoms on the relaxation processes of the 209Bi nuclear spin was observed for Bi4Ge3O12 crystals.

• Both weak external magnetic field and paramagnetic atoms inserted into the crystal lattice of Bi4Ge3O12 result in considerably increasing spin-spin relaxation time T2.

• In pure Bi4Ge3O12 crystal, intrinsic paramagnetic centers are found to exist which decrease the spin-lattice relaxation time T1 at low temperature.

• The crystal electric field splits the ground multiplet of the paramagnetic dopants and results in non-monotonous dependence of spin-lattice relaxation time T1 on temperature in the temperature interval 4.2-77 K.

2 2 2ˆ [3 ( 1) ( )]4 (2 1) 2

z zQ z

eQqH I I I I II I

Bi4Ge3O12

209Bi I = 9/2 H = 0

m

±9/2

±7/2

±5/2

±3/2

ν4

ν3

ν2

ν1±1/2